Processing method of thermoplastic polyester, thermoplastic polyester product and application of thermoplastic polyester product

Abstract

The invention provides a processing method of thermoplastic polyester, a thermoplastic polyester product and application of the thermoplastic polyester product. The processing method comprises the following steps: mixing thermoplastic polyester with a polyfunctional group cross-linking agent, and carrying out thermoplastic processing; 0.3-3 parts by mass of the polyfunctional group cross-linking agent is added into every 100 parts by mass of the thermoplastic polyester; the polyfunctional group cross-linking agent is a compound containing more than two functional groups capable of reacting with hydroxyl groups or a mixture thereof. The invention also provides a thermoplastic polyester product prepared by the processing method. The invention also provides application of the thermoplastic polyester product in preparation of a cable and / or an infusion tube. According to the processing method of the thermoplastic polyester provided by the invention, a small amount of cross-linking agent is added, so that the polyester structure is changed on the aspect of a finished product, and the chemical resistance of the finished product is improved.

Description

Technical Field

[0001] The present invention relates to a processing method of thermoplastic polyester, a thermoplastic polyester product and its application, belonging to the technical field of polyester materials. Background Art

[0002] Thermoplastic plastics, also known as thermosoftening plastics, refer to plastic high-molecular materials that become flexible or plastic when the temperature rises to a certain extent and solidify again after cooling. Thermosetting plastics refer to plastics that can be cured or have the characteristics of insolubility (or infusibility) under heat or other conditions, such as phenolic plastics, epoxy plastics, etc. Thermoplastic plastics become soft and flow when heated and harden when cooled; this process is reversible and can be repeated. Thermosetting plastics can be softened and flowed when heated for the first time. When heated to a certain temperature, a chemical reaction - crosslinking and curing occurs to harden; this change is irreversible. Then, when heated again, it can no longer be softened and flowed. Most polyester resins are thermoplastic materials. Thermoplastic polyesters are usually sold in the form of polyester resin particles, and downstream processing manufacturers can use various convenient processing means such as injection molding and extrusion to process the resin particles.

[0003] Since thermoplastic polyester particles cannot contain crosslinking and curing like thermosetting materials, some physical and chemical properties are slightly inferior to crosslinked materials. Especially the anti-solvent dissolution property (chemical resistance) is greatly affected by the type of polyester monomer and the type of solvent. Especially for thermoplastic polyester elastomers, the amorphous part contained in thermoplastic polyester elastomers is usually the polyether segment. For example, as disclosed in CN1969012A, an increase in the proportion of the amorphous part will lead to an increase in elasticity and flexibility, but also lead to a decrease in plasticity, mechanical strength, dimensional stability and oil resistance. For example, although the thermoplastic polyester elastomer Hytrel 4056 has good resistance to strong polar solvents such as methanol and ethanol, its anti-solvent property to solvents such as acetone is poor, which limits the application range of this material, especially in the fields of infusion tubes, special cables and solvent-resistant conveyor belts with high chemical resistance requirements.

[0004] The technical solution disclosed in JP1982102927A adds copper powder to the linear polyester resin to play a crosslinking role in a hot oxygen environment, improving the chemical resistance and heat resistance of the polyester. However, copper powder may cause great damage to the resistance isolation performance of the product. Summary of the Invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a processing method of thermoplastic polyester. This processing method modifies the thermoplastic polyester during the processing stage, and can effectively improve the chemical resistance of the obtained finished product.

[0006] The present invention also provides a thermoplastic polyester product obtained by the above processing method.

[0007] To achieve the above object, the present invention provides a processing method of thermoplastic polyester, wherein the processing method includes the step of mixing the thermoplastic polyester with a polyfunctional crosslinking agent for thermoplastic processing;

[0008] 0.3 - 3 parts by mass of the polyfunctional crosslinking agent is added to every 100 parts by mass of the thermoplastic polyester;

[0009] The polyfunctional crosslinking agent is a compound or a mixture thereof containing more than 2 functional groups capable of reacting with hydroxyl groups.

[0010] In the above processing method, preferably, the gel content of the product of the thermoplastic processing is ≥5%, preferably ≥30%.

[0011] In the above processing method, preferably, the average functionality of the polyfunctional crosslinking agent is not less than 2.4, more preferably not less than 2.7.

[0012] In the above processing method, preferably, the thermoplastic polyester is one or a combination of two or more of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and thermoplastic polyester elastomer (TPEE).

[0013] In the above processing method, preferably, the functional group capable of reacting with hydroxyl groups is an isocyanate group.

[0014] In the above processing method, preferably, the polyfunctional crosslinking agent is one or a combination of two or more of polymethylene polyphenyl polyisocyanate (PM), hexamethylene diisocyanate (HDI) trimer, and hexamethylene diisocyanate biuret.

[0015] In the above processing method, preferably, the thermoplastic processing is injection molding, extrusion, blow molding, blown film, etc.

[0016] In the above processing method, preferably, the operation of mixing the thermoplastic polyester with the polyfunctional crosslinking agent is carried out before the thermoplastic processing, or during the thermoplastic processing.

[0017] In the above processing method, other resins and / or additives can also be added during processing.

[0018] The present invention also provides a thermoplastic polyester product prepared by the above processing method.

[0019] According to the specific embodiments of the present invention, preferably, the N element content of the thermoplastic polyester product is 80 ppm - 2500 ppm.

[0020] According to a specific embodiment of the present invention, preferably, the gel content of the thermoplastic polyester product is ≥5%, preferably ≥30%.

[0021] The present invention also provides the use of the above thermoplastic polyester product in the preparation of cables and / or infusion tubes.

[0022] The processing method of the thermoplastic polyester provided by the present invention changes the polyester structure at the finished product level by adding a small amount of crosslinking agent, and improves the chemical resistance of the finished product.

[0023] After the products of the present invention are processed and formed by extrusion, injection molding, etc., the hydroxyl groups remaining at the ends of the polyester macromolecules react with the crosslinking agent to form a branched structure, increase the molecular weight of the product, and form a certain amount of crosslinked gel structure. Therefore, the chemical resistance such as solvent resistance of the product is significantly improved.

[0024] By increasing branching, increasing the molecular weight, and reducing free ends, the chemical resistance can be improved to a certain extent. Further, when the branching sites are sufficient, a network crosslinking is formed between the polymer chains, becoming insoluble and at most only swellable gel structure. The higher the gel content, the higher the crosslinking density, and the better the chemical resistance. However, the gel structure cannot be processed by thermoplastic methods, and with the increase of the gel content, the viscosity increases sharply. Therefore, it is necessary to control the gel content of the resin during the processing stage. Experiments show that when the gel content reaches more than 5%, there is an obvious improvement in solvent resistance. With the increase of the gel content, the extrusion pressure and energy consumption required by the extruder increase continuously. When the gel content is increased to more than 30%, the solvent resistance still improves with the increase of the gel content, but the processing energy consumption increases sharply.

[0025] It should be noted that it is estimated that the gel content in the tested product is much greater than the gel content of the resin during the processing, because the temperature is extremely high during the processing, and the obtained product is still within the appropriate reaction temperature of the isocyanate when it exits the processing section of the extruder / injection molding machine and has not been fully cooled. Therefore, there is a delayed reaction, and the gel content is extremely sensitive to the reaction degree. A small amount of continued reaction may greatly increase the gel content obtained by testing.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. The processing method of the thermoplastic polyester provided by the present invention can improve the chemical resistance of the processed finished product.

[0028] 2. The method provided by the present invention has the advantages of simple operation and can utilize existing equipment, has broad application prospects, and contains huge economic benefits. Specific Embodiments

[0029] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the following detailed description of the technical solution of the present invention is provided, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0030] Solvent resistance test method:

[0031] All samples shall be stored at room temperature for 24 hours or more before sampling;

[0032] Cut 3 - 5 g of the sample to be tested and weigh it, denoted as m 0 , completely immerse it in the solvent / solution to be tested and seal the test tube / glass bottle, place it on a constant temperature shaker at the temperature to be tested (30 °C if not otherwise specified) for 72 hours. If the appearance of the sample is intact, take out the sample, quickly dry the surface with filter paper and then quickly weigh it, denoted as m 1 ;

[0033] Calculate the solvent absorption rate as (m 1 - m 0 ) / m 0 ×100%;

[0034] The same sample to be tested is sampled and tested 3 times in parallel, and the average value is taken.

[0035] For samples with broken or dissolved appearance and unable to be taken out for weighing, record them as having a broken or dissolved appearance, and no longer test the solvent absorption rate.

[0036] It is observed in the test that for some solvents, the appearance (thickness) of the sample has an impact of more than 10% on the test results. Therefore, the samples to be tested and the comparison samples should have the same appearance and be close in weight (deviation < 10%), and it is preferred to test thin-layer / thin-wall products. The mass of the solvent / solution to be tested should be more than 10 times that of m 0 . If the test result is a broken appearance, use 100 times m 0 for retesting. If the test result is dissolution, no retesting is required.

[0037] Test method for gel content:

[0038] All samples shall be stored at room temperature for 24 hours or more before sampling.

[0039] Weigh the filter element of the Soxhlet extractor, denoted as m 1 , cut 1 - 2 g of the sample to be tested and weigh it, denoted as m 2 , place it in the Soxhlet extractor, use chloroform as the solvent, and heat and reflux for 6 hours. After taking out the filter element, first air dry it at room temperature for 1 hour, and then dry it in a vacuum oven at 60 °C for 24 hours. The total weight of the filter element and the remaining sample is m t . The gel content is (m t - m 1 ) / m 2 ×100%.

[0040] Unless otherwise specified, the raw materials used in the examples or comparative examples are all commercially available. Both self-made and commercially available polyester resin particles need to be stored in a desiccator.

[0041] Preparation Example 1:

[0042] In a 15L polymerization reactor, add 3.25 kg of terephthalic acid (PTA), 3 kg of 1,4-butanediol (BDO), 1.85 kg of polytetramethylene ether glycol (PTMEG, number average molecular weight 1000), with the addition amount being about 30% of the theoretical mass of the product to be prepared. Add 45 g of antioxidant (BHT) and 4 g of tetrabutyl titanate; displace with nitrogen 3 times;

[0043] Gradually heat up to 220 °C under 80 kPa (absolute pressure) for the esterification reaction. The esterification reaction takes 180 - 240 minutes. After the water output slows down (about 1600 g), raise the internal temperature of the reactor to 245 °C, reduce the pressure to below 50 Pa in about 30 minutes, and continue the polycondensation reaction for 60 - 120 minutes. After observing that the torque of the reactor rises to the target value, obtain the target polyester elastomer, denoted as polyester A1.

[0044] Preparation Example 2:

[0045] In a 15L polymerization reactor, add 2.5 kg of terephthalic acid (PTA), 2.5 kg of 1,4-butanediol (BDO), 2.21 kg of polytetramethylene ether glycol (PTMEG, number average molecular weight 2000), with the addition amount being about 45% of the theoretical mass of the product to be prepared. Add 55 g of antioxidant (1010) and 3.5 g of tetrabutyl titanate; displace with nitrogen 3 times;

[0046] Gradually heat up to 220 °C under 80 kPa (absolute pressure) for the esterification reaction. The esterification reaction takes 180 - 240 minutes. After the water output slows down (about 1300 g), raise the internal temperature of the reactor to 245 °C, reduce the pressure to below 50 Pa in about 30 minutes, and continue the polycondensation reaction for 90 - 150 minutes. After observing that the torque of the reactor rises to the target value, obtain the target polyester elastomer, denoted as polyester A2.

[0047] Comparative Example 1 & Example 1

[0048] Add 2 kg of polyester A1 to the hopper of the extruder. Set the feeding speed at 2 kg / 30 min, the temperature of the front section of the extruder at 235 °C, the middle section at 235 °C, the rear section at 220 °C, the die head temperature at 220 °C, and the rotation speed at 125 rpm. First, without adding a crosslinking agent, extrude the pipe (inner diameter about 7 mm, outer diameter about 8.5 mm) for about 10 minutes, and take the middle section sample as the sample of Comparative Example 1;

[0049] Then, WANNATE PM200 (average NCO functionality is about 2.7; Yantai Wanhua Chemical) was added at a rate of 6 g / 30 min to the fifth section of the extruder and continuous extrusion was continued. The samples in the first 10 minutes were regarded as transition materials and discarded, and the samples in the last 10 minutes were taken as the samples of Example 1. The middle-section samples were taken for testing. The gel content of the product of Example 1 was 5%.

[0050] The solvent resistance properties of Example 1 and Comparative Example 1 were tested in isopropyl alcohol in the same way and at the same ratio.

[0051] The test results showed that the 72-hour isopropyl alcohol absorption rate of the sample of Example 1 was 7.5%, and the 72-hour isopropyl alcohol absorption rate of the sample of Comparative Example 1 was 22%.

[0052] Comparative Example 2 & Example 2

[0053] 2 kg of polyester A2 was added to the hopper of the extruder. The feeding speed was set at 2 kg / 30 min. The temperature of the front section of the extruder was 235 °C, the middle section was 235 °C, the rear section was 220 °C, the die head temperature was 220 °C, and the rotation speed was 125 rpm. First, no cross-linking agent was added, and the pipe (inner diameter is about 7 mm, outer diameter is about 8.5 mm) was extruded for about 10 minutes. The middle-section samples were taken as the samples of Comparative Example 2;

[0054] Then, HDI trimer was added at a rate of 20 g / 30 min to the fifth section of the extruder and continuous extrusion was continued. The samples in the first 10 minutes were regarded as transition materials and discarded, and the samples in the last 10 minutes were taken as the samples of Example 2. The middle-section samples were taken for testing. The gel content of the product of Example 2 was 17%.

[0055] The solvent resistance properties of Example 2 and Comparative Example 2 were tested in diethyl ether in the same way and at the same ratio (the test temperature was room temperature, and the constant temperature shaker temperature control function was not used).

[0056] The test results showed that the 72-hour diethyl ether absorption rate of the sample of Example 2 was 350%, and the sample of Comparative Example 2 was broken after 72 hours. The sample with 100 times the m 0 mass was retested, and the result was still that the sample was broken.

[0057] Example 3

[0058] 2 kg of Hytrel 4056 (TPEE, DuPont, USA) was mixed evenly with 60 g of HDI biuret and added to the hopper of the injection molding machine to injection mold into a test specimen bar of Type II specimen of GB1040-92 standard. The melt temperature of the injection molding machine was 180 °C, and the mold temperature was 40 °C. The gel content of the product of Example 3 was 39%.

[0059] Comparative Example 3

[0060] Add 2 kg of Hytrel 4056 to the hopper of the injection molding machine and injection mold it into test specimens of Type II specimens according to the GB1040-92 standard. The melt temperature of the injection molding machine is 180 °C and the mold temperature is 40 °C.

[0061] Test the solvent resistance characteristics of Example 3 and Comparative Example 3 in acetone in the same ratio and by the same method.

[0062] The test results show that: the ether absorption rate of the sample in Example 3 after 72 h is 180%, the sample in Comparative Example 3 was broken after 72 h, and the sample was redetected using a sample with 100 times the mass and the sample dissolved. 0 The sample was redetected using a sample with 100 times the mass and the sample dissolved.

[0063] It can be seen from the comparison of the above examples and comparative examples that under the condition of the same starting polyester raw materials, by mixing a crosslinking agent before processing or during the processing, the chemical resistance of the finished product is significantly improved.

[0064] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Those skilled in the art should be able to simply infer that the above processing method can also affect other properties while improving chemical resistance, such as affecting the water vapor transmission rate (the water vapor transmission rate can be regarded as a special case of chemical resistance), abrasion, etc., and the advantages of the above processing method can be found through corresponding performance tests. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A processing method of thermoplastic polyester, wherein, the processing method includes the step of mixing the thermoplastic polyester with a multi-functional crosslinking agent for thermoplastic processing; 0.3 - 3 parts by mass of the multi-functional crosslinking agent is added to every 100 parts by mass of the thermoplastic polyester; the multi-functional crosslinking agent is a compound or a mixture thereof containing more than 2 functional groups capable of reacting with hydroxyl groups.

2. The processing method according to claim 1, wherein, the gel content of the product of the thermoplastic processing is ≥5%, preferably ≥30%.

3. The processing method according to claim 1, wherein, the average functionality of the multi-functional crosslinking agent is not less than 2.4, preferably not less than 2.

7.

4. The processing method according to claim 1, wherein, the thermoplastic polyester is one or a combination of two or more of polyethylene terephthalate, polybutylene terephthalate, and thermoplastic polyester elastomer.

5. The processing method according to claim 1, wherein, the functional group capable of reacting with hydroxyl groups is an isocyanate group.

6. The processing method according to claim 1 or 5, wherein, the multi-functional crosslinking agent is one or a combination of two or more of polymethylene polyphenyl polyisocyanate, hexamethylene diisocyanate trimer, and hexamethylene diisocyanate biuret.

7. The processing method according to claim 1, wherein, the thermoplastic processing is injection molding, extrusion, blow molding, or blown film.

8. The processing method according to claim 1, wherein, the operation of mixing the thermoplastic polyester with the multi-functional crosslinking agent is carried out before the thermoplastic processing, or during the thermoplastic processing.

9. A thermoplastic polyester product prepared by the processing method according to any one of claims 1 - 8.

10. The thermoplastic polyester product according to claim 9, wherein, the N element content of the thermoplastic polyester product is 80 ppm - 2500 ppm.

11. The thermoplastic polyester product according to claim 10, wherein, the gel content of the thermoplastic polyester product is ≥5%, preferably ≥30%.

12. Use of the thermoplastic polyester product according to any one of claims 9 - 11 in the preparation of cables and / or infusion tubes.